Subsurface Organic Fertilization Increases Ecosystem Multifunctionality and Sunflower Yield in Saline Soil

Abstract

Salt stress poses a growing constraint on crop productivity in arid regions worldwide. Previous evidence indicated that organic fertilization is a pivotal management practice for enhancing crop yield and soil fertility in agroecosystems. How organic fertilization depths influence the associations among soil health, ecosystem multifunctionality, and crop yield, however, still remains unclear. Thus, a 3-year field experiment was carried out to investigate the impacts of the application of humic acid and manure at 0-15 cm of surface and 15-30 cm of subsurface on soil quality index, enzyme activities, ecosystem multifunctionality, as well as crop yield in saline soils. Subsurface organic fertilization improved soil quality index between 0-45 cm soil by 20-47%, whilst surface organic fertilization improved soil quality index only at 0-30 cm by 15-51%. The higher soil quality under surface fertilization was characterized by an increase in soil organic carbon, available nutrients, and a decrease in electrical conductivity compared to surface fertilization. The application of organic fertilization promoted microbial diversity and richness, enzyme activities, and ultimately improved soil ecosystem multifunctionality. However, soil ecosystem multifunctionality was increased by 122-214% at 0-30 cm under subsurface organic fertilization, whilst it was increased by 178% only at 0-15 cm layer. Pairwise comparisons further confirmed that electrical conductivity and soil organic carbon were negatively and positively correlated with soil ecological functions between 0-45 cm, respectively. The higher soil quality and a microenvironment with higher ecosystem multifunctionality under subsurface fertilization increased sunflower yield by 16% and 8% as compared to chemical fertilizer only and surface fertilization, respectively. This probably because of the effective improvement in soil electrical conductivity, soil organic carbon, the activities of β-glucosidase, and diversity and richness of microbial resulted from deep fertilization. Overall, subsurface organic fertilization is an effective way to enhance soil ecosystem multifunctionality and crop yield in saline soils.

Keywords: Soil quality, Enzyme activity, Soil ecosystem multifunctionality, Sunflower yield, saline soil, Humic acid and manure